The sputtering technique is a film-forming technique with which a plasma is utilized to generate ions striking a sputtering target so as to result in atoms of the sputtering target depositing on a substrate as a film. The sputtering technique is particularly used to produce a metallic layer in various manufacturing processes used in the semiconductor and the photoelectric industries. The properties of films formed during sputtering is related to the properties of the sputtering target itself, such as the size of the respective crystal grain and the formation of secondary phase with distribution characteristics.
Various sputtering techniques are used in order to effect the deposition of a film over the surface of a substrate. Deposited metal films, such as metal films on a flat panel display device, can be formed by a magnetron sputtering apparatus or other sputtering techniques. The magnetron sputtering apparatus induces plasma ions of a gas to bombard a target, causing surface atoms of the target material to be ejected therefrom and to be deposited as a film or layer on the surface of a substrate. Conventionally, a sputtering source in the form of a planar disc or rectangle is used as the target, and ejected atoms travel along a line-of-sight trajectory to deposit on top of a wafer whose deposition face is parallel to the erosion face of the target.
However, a tubular-shaped sputtering target can also be used. In this case, the plasma is external and the atoms are sputtered from the exterior of the tube. The flat substrate is slowly passed over the target. Typically, its motion is horizontal, and in a direction at a right angle to the target axis, which is also horizontal. Thus the substrate can be gradually coated as it passes over the target.
In many cases, sputtering targets, particularly those containing molybdenum, have a wrought microstructure with non-uniform grain texture, which may change from one sputtering target to the next. These “non-uniformities” lead to non-uniform films being deposited onto substrates and devices, particularly flat panel displays that do not operate optimally.
In other cases, molybdenum-based sputtering targets are manufactured using a conventional thermomechanical working step. Unfortunately, this methodology generally induces heterogeneity of grain size and texture. The heterogeneity in the sputtering targets typically leads to sputtered films that do not possess the uniformity desired in most semiconductor and photoelectric applications.
In some applications, large plates of pure molybdenum are required as sputtering targets. In such cases, the production of large plates is accomplished through the machining and assembly of multiple plates, often referred to as segmented plates. The preparation of segmented plates requires an increased amount of machining and assembly cost compared to the production of a single plate ingot. Additionally, the assembly of different plates creates variability in the large segmented plate, which can cause unacceptable variability in films formed by sputtering the large plate target.
Therefore, there is a need in the art for molybdenum sputtering targets that overcome the deficiencies of the prior art and have a fine grain size and uniform grain texture.